1. Field of the Invention
The instant disclosure relates to a control apparatus for a fan motor, more particularly to a multi-speed control apparatus for the fan motor.
2. Description of Related Art
Refer to FIG. 1, which shows a circuit diagram of a control apparatus for the conventional fan motor. In the figure, a controller 10 is provided in the control apparatus 1 for driving a fan motor 12. This controller 10 may be implemented as an integrated circuit (IC) which has some contacts for connecting the circuits, such as the shown Hall element 14, a converter 16, etc. The Hall element 14 is usually used for detecting the state of rotation of the fan motor 12, and momentarily generates a feedback signal (not shown) to the controller 10.
The converter 16 is especially used to convert the pulse-width modulation signal (SPWM) input from some external elements including processor or IC into a voltage signal V1. The voltage signal V1 is then input into the controller 10. In general, the duty cycle of the pulse-width modulation signal may change due to the change (up or down) of temperature of the external devices depending on the environmental conditions and system of operation. Noted that the voltage signal V1 is determined based on the duty cycle of the PWM signal.
In other words, the controller 10 may change the rotating speed of the fan motor 12 anytime based on the change of the voltage signal V1. Thus, the rotating speed of the fan motor 12 may be modulated automatically due to some external conditions such as the temperature of the external devices.
However, the PWM signal generated by the external devices may not accurately present the real temperature. Further, the process of the converter 16 converting the PWM signal into the controller 10 readable voltage signal V1 may cause the voltage signal V1 to be distorted or delayed. In short, the controller 10 may not accurately control the rotating speed of the fan motor 12 to fit in with the need of heat dissipation by merely referring to the external PWM signal.